1. Field of the Invention
This invention relates to cameras, such as movie cameras and, particularly, to circuits for preventing faulty operation when the battery voltage falls.
2. Description of the Prior Art
Cameras with circuits for preventing faulty operation due to a drop in the battery voltage are known. Such circuits are used in the circuitry for controlling the operation of a cine camera and constructed in the form of a warning circuit using an indicator, such as an LED, that lights upon the fall of the battery voltage, or a switching circuit that responds to the fall of the battery voltage and cuts off the electrical power supply. Such conventional error preventing, i.e., faulty operation preventing, circuits are rendered effective just as soon as the battery voltage drops below the satisfactory operating level. This may result in a serious disadvantage, namely the circuit may respond with a warning or cut off the control when the effective voltage of the battery is only temporarily lowered, for example, due to a sudden increase of the load current. Specifically, the operation of a cine camera begins by supplying electrical power to the diaphragm control circuit and, after the diaphragm control is stabilized, proceeds to drive the film motor. Supplying a large current to the diaphragm control circuit temporarily lowers the battery voltage. A conventional circuit tends to cut off the electrical power supply in response to the temporary lowering of the battery voltage. Thus, even when the battery voltage recovers the satisfactory exposure operating level, the motor is no longer supplied with electrical power.
Another disadvantage of conventional circuits is that the error preventing operation occurring when the battery voltage falls is effected by merely opening the power switch to terminate the application of electric power supplied to all the circuit portions, so that the camera control circuit stops controlling the operation of the camera even in the middle of a cycle during the pulldown operation of the claw. In other words, for example, in the sequence control circuit of a sound motion picture camera, the actuation of release initiates an exposure not directly but through various control members driven in sequence according to a predetermined program. To terminate 20 the exposure, the camera must be stopped according to a given sequence, or otherwise the rotary shutter would be left open. Accordingly, if the drop in battery voltage occurs during an exposure, it is then necessary to extend application of the electrical power supply until the concurrent exposure terminating sequence has been completed. Alternately, when a drop is detected at the time the release is actuated, the electrical power supplied to the shutter control circuit should be instantly cut off, because the exposure aperture is still closed.